The invention relates to a diagnostic system and a diagnostic tester for checking motor vehicle control devices with which not only is it possible to find faults, as previously customary, but also with which it is likewise possible to check whether a repair which has been performed was successful. The diagnostic tester is likewise used to present a method for the improved checking of repairs. The diagnostic system and diagnostic tester correspond in particular to the legal requirements for diagnostic systems in the USA.
Diagnostic systems and diagnostic testers for motor vehicle control devices are nowadays predominantly computer based in motor vehicle workshops. BMW were leaders in the introduction of computer-based diagnostic testers in 1994 with the diagnostic system BMW-DIS which set the standard for contemporary diagnostic systems and diagnostic testers in motor vehicle workshops. This system is described, for example, in the vocational training manual by Rauner/Schreier/Spöttel: “Die Zukunft computergestützter Kfz-Diagnose [The future of computer-supported motor vehicle diagnostics]” published by Bertelsmann in Bielefeld, 2002, ISBN 3-7639-3022-1. The following diagnostic testers have repeatedly resorted to the basic structure of this diagnostic system. For example, there is also a German patent application by Bosch, DE 199 21 845 A1 which is mentioned here by way of example because it summarizes this basic structure in a particularly concise and brief way. A diagnostic test device for motor vehicles is described in which programmable control devices are provided with self-diagnostic means in the motor vehicle, said means using program control to control and monitor the engine controller and other systems of the motor vehicle, generate fault codes and store them and said means can be connected to an external diagnostic tester via a motor vehicle-mounted diagnostic/test plug. The invention is also based on such a basic structure for a diagnostic tester.
The interface or the diagnostic plug for connecting an external diagnostic tester to the motor vehicle-mounted control devices was in the past, and is to a certain extent still today, the object of efforts at standardization. In particular in the USA these efforts at standardization with which access to motor vehicle-mounted control devices, and thus the ability to perform diagnostics on them, is made possible and regulated, still involve measures by legislators. A standard which has become established is referred to as the keyword protocol 2000. The standardization bases for this keyword protocol 2000 can be found in the international standard ISO 14 230-3, which is concerned with the application layer, and in ISO 14 230-2 which is concerned with what is referred to as the data link layer. A supplementary standard on which the keyword protocol 2000 is based and which has become a component of the above-mentioned standards is the service vehicle standard SAE J1979. In particular the possibilities for reading out the data memories in the control devices which are provided for a diagnostic tester by the keyword protocol 2000 are significant for the invention described here.
Known diagnostic systems and diagnostic testers are restricted to reading out existing fault codes from the control devices in the motor vehicle, processing and interpreting them with a diagnostic program and displaying the result of this interpretation on a screen of the diagnostic tester. In the motor vehicle workshop, a motor vehicle mechanic then works through the displayed list of deficiencies, during which process he can call up further information about the individually specified deficiencies using the diagnostic tester. In this context, further technical information resources such as technical drawings and of course the repair instructions with which he can eliminate the detected fault are of particular interest for him. If the motor vehicle mechanic has worked through the list of deficiencies, he uses the diagnostic tester to clear the stored and read-out fault codes in the motor vehicle-mounted control devices and in the diagnostic tester itself. Final checking as to whether the repairs which have been performed were successful or whether consequential faults have arisen as a result of the repair, is performed with a final test drive depending on the working organization in the motor vehicle workshop. Diagnostic systems and diagnostic testers which are known to the patent applicant do not support the quality checking of the repairs performed. They are not suitable for this either since the list of deficiencies and the fault codes in the control devices are cleared by the motor vehicle mechanic by a clear command. Of course, as a result the information about a malfunction which has occurred once and been detected is lost. Therefore, until now a diagnostic tester did not provide a motor vehicle mechanic with any support as to whether or not his repair was successful.
Taking the previously described prior art as a starting point, the aim of the invention is therefore to specify a diagnostic system and a diagnostic tester which permit improved checking of repairs using the diagnostic tester. Particular emphasis is placed here on the legal prohibition to clear individual faults in control devices relating to exhaust gas in the USA.